open a new window using struts2 button

I am working on struts2. I have an web page where there is an text box to enter the username and click the button 'search' to search the user whose name is starting with the letter that is typed in that text box. when the user clicks on the button 'search' an new window will be opened , there i will be displaying the names in the dropdown box. the user can select a name from that drop down box, and click on the button 'Ok'. If the user clicks on the button 'Ok' , that window should be closed and the value that is selected in that drop down box should be passed to the previous web page, and displayed in that textbox. I am new to programming. Please some one help me... Please give me some ideas...

Welcome to the JavaRanch
That's a pretty ambitious use case for someone who is new to programming. How about displaying one page with a search entry, display a new page for the search results, then a third with the selected value and whatever else you need entered? This would be much easier to implement.
If you absolutely need to implement the functionality you specified, here is an example on how to open a new window with JavaScript. You'll have to use JavaScript to set the value back on the page. There are plenty of JavaScript tutorials available, as well as our own JavaScript forum to help you along.